newman



Jan. 24, 1956 E. A. NEWMAN 2,732,440

ELECTRONIC PULSE OUTPUT CIRCUITS Filed Jan. 8, 1951 2 Sheets-Sheet l By Inventor F/ 2 Jan. 24, 1956 E. A. NEWMAN 2,732,440

ELECTRONIC PULSE OUTPUT CIRCUITS Filed Jan. 8, 1951 2 Sheets-Sheet 2 ,A F 9- 3 68 n vVVW\/\r F p our R2 R4 IOOK iz-zk EDWARD A. NEWMAN F 4 -3o0 +100 soo +/oo Inventor y w m 4', Attorneys Un d ee a ELECTRONIC PULSE OUTPUT CIRCUITS Edward Arthur Newman, Teddington, England, assignor to National Research Development Corporation, London, England, a corporation of Great Britain Application January 8, 1951, Serial No. 205,004

Claims priority, application Great Britain January 14, 19 50 3 Claims. (Cl. 179-171) The invention relates to electronic pulse output circuits in which it is desired to drive pulses having short times of rise and fall into frequency dependent loads", for example, capacitative loads and unterminated or incorrectly terminated lines. i

In a particular case, 15 volt pulses with a time of rise of .05 miscrosecond have to be fed into a capacitor of the order of 1,000 micromicrofarads.

One known method of doing this is by means of a conventional cathode follower valve but this method suffers from the disadvantages that the cathode follower has to pass a very large current and that the output amplitude is dependent on the characteristics of the valve. (In the particular case mentioned above, the current would be of the order of 500 milliamps.)

It is anobject of the present invention to provide a circuit by means of which pulses having a short time of rise and fall may be fed into relatively large capacitors or similar frequency dependent impedances, said circuit having a low output impedance and producing an output whose amplitude is substantially independent of the characteristics of the valve used in the circuit and in which the valve does not need to pass a very large current.

According to the present invention, there is provided a circuit for feeding pulses having short times of rise or fall into frequency dependent impedances, the said circuit comprising a thermionic valve to the control grid of which an input is arranged to be fed, a resistance in the cathode circuit of the said valve across which the output is developed, a step-down transformer having its primary winding in the anode circuit of the said valve and its secondary winding arranged to feed, through a network having a low impedance at high frequencies and a high impedance at low frequencies, an output across the said resistance.

According to one embodiment of the invention, there is provided a circuit comprising a pair of triode valves having a common cathode load arranged so that a pulse supplied to the grid of one valve produces a corresponding pulse at the anode of the other valve, a first cathode follower valve fed by one of the said pair of triode valves and a second cathode follower valve across the cathode of which the output is to be taken, a step-down transformer having its primary winding in the anode circuit of the said second cathode follower valve and its second ary winding arranged to feed an output across the cathode resistance of the said second cathode follower valve through a network having a low impedance at high frequencies and a high impedance at low frequencies with means for feeding a fraction of the output from said second cathode follower valve back to the grid of the triode valve in the said pair which feeds the said first cathode follower valve. 4

Reference is now made to the accompanying drawings in which:

Figure 1 is a circuit diagram showing one embodiment of the invention,

Figure 2 is a circuit diagram showing a further embodiment of the invention,

Figure 3 shows how the embodiment shown in Figure 1 or Figure 2 may be used for feeding a set of transmission lines, and

Figure 4 shows a circuit which is a modification of Figure 2.

In the circuit of Figure l the input is applied to the control grid of the valve V. A step-down transformer T in the anode lead has its secondary winding connected to earth and to an impedance Z. Z is a low impedance at high frequencies .and a high impedance at frequencies where the primary inductive impedance of the transformer would be too high to enable the pulse to be sustained. The other end of the impedance Z is connected to the cathode of the valve and the output is taken across a high resistance L in parallel with the high capacitative load C. High frequency currents from the transformer are used to reinforce the cathode current when the load impedance is low, but the cathode current alone provides the output when the load impedance is high. The output amplitude is substantially equal to the input amplitude as in a normal cathode follower.

In Figure 2 there is shown a preferred embodiment of the invention in which the input signal is fed onto the control grid of VIA which is one half of the double triode (VIA and VIB). The output from VIB anode is fed onto the control grid of V2 which is connected up as a conventional cathode follower valve. The output from the cathode V2 is fed onto the grid of V3 which is connected up in a similar manner to the valve in-Figure 1 described above. The step-down transformer T1 has a ratio of 4.5 to 1 and the output is taken across the 2.2 k. resistance R4. The impedance network (corresponding to Z in Figure l) is C2, C3, and R5 and the resistance chain R1, R2 enables a fraction of the output to be fed back to the grid of VIB.

Suitable values of components are shown in Figure 2. The output pulse amplitude is (R1+R2)/R2 times the input pulse amplitude. This embodiment may be modified to operate as a direct current amplifier in which case the coupling condensers are omitted and the grid biases suitably adjusted.

The output impedance of the circuits illustrated is very low andv they may be used to feed a number of low impedance lines, for example, three 68 ohm lines may be coupled to the output in the manner shown in Figure 3 in which the live conductors of the three lines are connected through separate 68 ohm resistors to the cathode of the output valve. Since the output impedance of the circuit is very low, these lines will be effectively terminated by 68 ohms at the drive end. They must be left unterminated at the far end.

What I claim is:

1. A circuit for feeding pulses having short times of rise or fall into frequency dependent impedances, said circuit comprising a thermionic valve having means to feed said pulses to the grid thereof, a resistance in the cathode circuit of said valve across which the output is developed, a step-down transformer having a primary winding in the anode circuit of said valve and a secondary winding, a network having a low impedance at high frequencies and a high impedance at low frequencies, means to feed the output of said secondary winding to said network and means to feed the output of said network to said cathode resistance and means to take the output of said circuit from across said cathode resistance, the said transformer being connected in such a sense that its output is substantially in phase with the signal on the cathode resistance.

2. A circuit for feeding pulses having short times of rise or fall into frequency dependent impedances, said circuit comprising a pair of triode valves, said valves having a common cathode load, means to feed said pulses to the grid of one valve whereby corresponding pulses are thereby produced at the anode 'of the other valve, a first cathode follower valve, means to feed the output of one of said triode valves to said first cathode'follower valve, a second cathode follower valve having a resistance in the cathode circuit thereof,- means to feed the cathode output voltage of said first cathode follower valve to said second cathode follower valve, a step-down transformer having a primary winding in the anode circuit of said second cathode follower valve and a secondary winding, a network having a low impedance at high frequencies and a high impedance at low frequencies, means to feed the output of said secondary winding to said network, means to feed the output of said network across said cathode resistance of said second cathode follower valve, means to feed a fraction of the output across said cathode resistance to the grid of said one triode valve, and means to take the output of said circuit from across said cathode resistance.

3. A circuit as claimed in claim 2, in which the said pair of triode valves and the two said cathode follower valves are connected to operate as a direct current transducer.

References Cited in the file of this patent UNITED STATES PATENTS 2,058,883 Ives et al Oct. 27, 1936 2,240,715 PercivaL; May 6, 1941 2,273,619 Bruck Feb. 17, 1942 2,302,798 Percival Nov. 24, 1942 2,305,403 Bartelink Dec. 15, 1942 2,383,867 Koch Aug. 28, 1945 2,429,775 Seright Oct. 28, 1947 FOREIGN PATENTS 50,851 Netherlands Sept. 15, 1941 

